The invention relates to a main element of an electric machine which comprises several winding strands with electric coils which are interconnected so as to be electrically conductive and a winding core with grooves lined up next to each other through which coils of the winding strands run.
A main element of an electric machine is understood to mean a stator or a rotor of the electric machine. An electric coil comprises several windings of electrical conductors arranged immediately adjacent to and/or on top of each other and electrically interconnected in series or of so-called combined electrical conductor elements arranged adjacent to and/or on top of each other, which are connected electrically in parallel and have the same or a different design with respect to their geometric structure and/or their diameter. A winding strand is understood to mean coils electrically interconnected in series and/or connected in parallel which are supplied with currents in phase. A winding of a main element of a multi-phase electric machine therefore has a number of winding strands consistent with the number of phases, wherein each winding strand is connected to an external conductor.
The individual coils of a winding strand of a main element are frequently distributed in grooves of a hub of the main element, for example, in grooves of a stator core, so that each coil runs through two grooves. As a rule, the grooves are arranged in a row next to each other in a surface facing an air gap between a stator and a rotor of the electric machine. The two grooves traversed by a coil may be immediately adjacent or grooves may be located between them through which other coils run (so-called distributed winding). Furthermore, a winding may be designed as a so-called single layer winding in which only precisely one coil runs through each groove, or as a so-called two-layer winding in which precisely two different coils run through each groove.
In a two-layer winding the two coils running through a groove may pertain to the same winding strand or to different winding strands. As a rule, the volume of each groove is divided by an electrically insulating partition wall into two areas of roughly the same size through which one of the two coils running through the groove runs respectively. A first of these areas extends from the base of the groove to the partition wall and contains the so-called lower layer of the groove which is formed by the coil running through the first area. The second area extends from the partition wall to the opening of the groove in the surface of the hub and contains the so-called upper layer of the groove which is formed by the coil running through the second area. Usually each coil of a two-layer winding forms a lower layer of a first groove through which it runs and an upper layer of the second groove through which it runs.
In a distributed two-layer winding, as a rule the coils must be created individually on account of their coil overlap. A coil is, for example, retracted mechanically. Retraction of a coil is understood to mean that, for example, with the aid of a template, a loose, pre-wound coil is retracted into grooves in a single operation.